The invention relates to a method and to a voltage supply circuit for producing a supply voltage from a relatively high supply voltage.
Voltage supply circuits and voltage or current supply modules such as these are used, for example, in vehicle technology.
The change in the vehicle power supply system voltage from 12 volts to 42 volts in future passenger vehicles and at the same time a requirement for a supply voltage for controllers, that is to say using digital circuit technology, at a known voltage of, for example, 5 volts, 3.3 volts or else 2.5 volts, is resulting in a number of problems.
By way of example, the linear fixed voltage regulators which are used in a 12 volt vehicle power supply system architecture for producing a previously normal supply voltage of 5 volts cannot be used owing to the considerably greater voltage difference that will occur in future passenger vehicles and the power loss that this will result in the linear regulator, since it will then no longer be possible to use these without additional cooling measures which, disadvantageously, would result in considerable additional costs. It is likewise impossible, for cost reasons, to use specific, expensive linear regulators optimized for this purpose.
A further requirement in vehicle technology is that some digital circuits or controllers, for example the controller which is responsible for central locking, remote control etc., need to operate in a daytime mode as well, in which the vehicle is in some circumstances parked for a lengthy time. This situation is taken into account by means of a standby mode for some controllers which have to remain active at least cyclically, while other controllers, which are not required, are switched off completely. The standby current in an operating mode (parking mode) such as this is in the xcexcA range, for example about 100 xcexcA, in contrast to a normal mode in the mA range, for example about 200 mA.
In order to reduce the thermal power loss in linear regulators, EP 0 805 540 A1 therefore proposes that a DC/DC converter be connected upstream of the linear regulators, in this way reducing the current consumption from the battery as well as the (thermal) power loss.
However, this circuit (which is used in a conventional 12 volt vehicle power supply system architecture) still has the disadvantage when used in a vehicle power supply system with a higher voltage, such as 42 volts, in that, in consequence, it is no longer possible to satisfy the standby current requirement in a parking mode, at least without using undesirable costly special components or cooling measures.
The present invention is therefore based on the object of providing a method for producing a supply voltage as well as a voltage supply circuit for carrying out such a method, which methods also satisfy the standby current requirement in a parking mode or standby mode in a cost-effective and simple manner.
According to the invention, this object is achieved by a method for producing a supply voltage, in particular for digital circuits, in a motor vehicle from a relatively high input voltage of more than 12 volts, in particular from a vehicle power supply system voltage of 42 volts,
a) in which an intermediate voltage at a level between the vehicle power supply system voltage and the supply voltage is produced from the vehicle power supply system voltage in a normal mode by means of a DC/DC converter, and
b) the supply voltage is produced from the intermediate voltage by means of at least one linear regulator, wherein
c) the DC/DC converter is switched off and is bridged by means of a bypass circuit in a parking mode, so that the supply voltage is produced directly by the at least one linear regulator.
The object can further be achieved by another method for producing a supply voltage during a first and second operation mode from a relatively high input voltage comprises the steps of:
a) during the first operation mode:
generating an intermediate voltage at a level between the high input voltage and the supply voltage from the high input voltage in a normal mode by means of a first converter, and
generating the supply voltage from the intermediate voltage by means of at least a second converter,
b) during the second operation mode:
switching off the first converter and bridging the first converter by means of a bypass circuit, so that the supply voltage is produced directly by the at least one second converter.
One embodiment is a voltage supply circuit having at least one linear regulator and having a DC/DC converter which is connected upstream of the at least one linear regulator, in order to produce a relatively low supply voltage, in particular for digital circuits, via an intermediate voltage from a voltage of more than 12 volts, in particular from a vehicle power supply system voltage of 42 volts, characterized in that the voltage supply circuit has a bypass circuit in order to bridge the converter in a parking mode.
Yet another embodiment is a voltage supply circuit having two operation modes comprising:
a first converter receiving a high supply voltage generating an intermediate voltage;
a second converter receiving the intermediate voltage for generating a supply voltage;
a control circuit for either turning on the first converter or for turning off the converter and feeding the high supply voltage directly to the second converter.
The control circuit may comprise a bypass circuit for bridging said first converter and may further comprises a current sensor for sensing the output current of the first converter to switch from the first to the second operation mode. The first converter can be a DC/DC converter and the second converter can be a linear regulator.
Since, according to the invention, the supply voltage or output voltage for digital circuits, in particular at a level of 5 volts, 3.3 volts, 2.5 volts or less, is produced solely by one or more linear regulators in a standby mode, the requirement for a very low standby current in the xcexcA range can be satisfied, since the power loss in a linear regulator remains with a low supply current in the xcexcA range even when there is a relatively large voltage difference between the input and output or supply voltage, and hence only insignificantly increases the standby current, which is already produced or consumed by the controller in the standby mode, to an overall standby current.
According to the invention, this is achieved by bridging, for example by means of a bypass circuit and in particular bypass transistor, the converter which is connected upstream of the linear regulator or the linear regulators, in which case the converter can advantageously be switched off in this mode, in order to further reduce the current consumption.
A wide range of different implementation options may be used for bridging the converter and for switching it off and on, for example coupling to the ignition lock or to a controller which is responsible for this, or coupling it to other events which may possibly be linked to one another and by means of which it is possible to distinguish between a standby or parking mode and a normal mode.
In one embodiment of the invention, the activation as well as the deactivation of the bypass, and, possibly, additionally the associated switching on and off of the converter, are carried out by means of a load current threshold value switch, which switches the converter on and the bypass off when the load current in the output or supply circuit, or a value which is proportional to thisxe2x80x94for example a load current threshold value in the intermediate circuit or side circuits from itxe2x80x94exceeds a predefined threshold value, and switches the bypass on and the converter off when the threshold value (parking mode) is undershot.
In another embodiment of the invention, the bypass and the converter are controlled by a microcontroller to which events such as xe2x80x9ccontroller switching to the standby modexe2x80x9d, xe2x80x9cengine switched offxe2x80x9d, xe2x80x9ccurrent regulator between the battery and the generator switched to battery modexe2x80x9d etc. are supplied as a signal, so that the control of the bypass and of the converter is dependent on one event on its own or in a specific combination (by means of appropriate software).
In the preferred embodiment according to the invention, this control function is carried out by means of a wake-up ASIC, which can carry out the same tasks in the same way as described above for the microcontroller but, in contrast to the microcontroller or microprocessor, depends directly on the vehicle power supply system voltage instead of on the supply voltage of the voltage module in the standby mode and, in consequence, can provide a standby mode even when not only the converter but also the linear regulators are completely switched off.
In the preferred embodiment according to the invention, different supply voltages can be produced by means of a number of linear regulators from the intermediate voltage which is produced by the converter in order, for example, to appropriately supply different circuit groups of a controller with different input voltages. In this case, the linear regulators may be followed by a logic circuit, which monitors the output voltages and/or supply voltages and produces a reset signal when a specific error or fault occurs, and switches off one or all of the output voltages depending on the requirements of the microcontroller that is used. Further advantageous refinements of the invention can be found in the dependent claims.